1. Field
The following description relates to an optical apparatus, and more particularly, to an optical probe which is inserted into a tube to pick up an image.
2. Description of the Related Art
In the field of medical imaging, a need for tomography to obtain an image of an inner portion of tissue surface with a high resolution along with information on blood vessels or tissue surface of internal organs is increasing. Specifically, since most cancer cells start from epithelial cells and spread to the inside of dermal cells in which blood vessels are located, cancer cells of very small size (50˜100 μm) in the early stage need to be detected in the epithelial cells to drastically reduce damage from the cancer, and to this end, a high-resolution tomography apparatus is required.
Typical magnetic resonance imaging (MRI) or computerized tomography (CT), and supersonic wave imaging may obtain a cross-sectional image of an organ through the use of waves that penetrate the skin. However, these techniques generate an output with a low resolution and thus are of limited use in detecting the early-stage, small cancer cells. In addition, optical coherence tomography (OCT) which has been recently implemented employs light that penetrates less deeply, i.e., only about 2˜3 mm, into the skin, compared to the other existing imaging techniques. OCT, however, has a resolution ten times higher than that of the other imaging techniques, and thus can provide an enhanced probability of detection of early-staged cancer. However, since OCT techniques result in resolutions lower than that of a microscope, it cannot be a substitute for biopsy or histology for determining the presence or existence of real cancer cells.
Optical probes are inserted into tube-shaped internal organs such as blood vessels and obtain cross-sectional images of tissues or of inner sides of the organs. The optical probes may be used for other purposes, such as non-destructive internal instruction, in addition to medical purposes. An optical probe includes an optical system therein, and optical systems for use to obtain images to substitute for biopsies or histologies are required to have a relatively low depth of field (DOF), and a relatively high horizontal resolution. Further, like other imaging apparatuses, optical probes should be capable of picking up cross-sectional images of deep inside tissues with a high depth of field. However, the depth of field is in inverse proportion to a horizontal resolution, and an optical system with low numerical aperture (NA) is required to increase the depth of field as in OCT whereas an optical system with high NA is required to acquire high horizontal resolution.